Recent years, MRAMs (Magnetic Random Access Memories) utilizing a TMR (Tunneling Magneto Resistive) effect have been developed. Having large magnetic resistance change ratios, magneto resistive elements including MTJs (Magnetic Tunnel Junctions) are used in MRAMs.
With the miniaturization of memory cells in MRAMs, a structure in which magneto resistive elements are provided on contact plugs is now being studied. In such a structure, the reliability of each magneto resistive element depends on the flatness of the corresponding contact plug.
Meanwhile, in the process of forming contact plugs in contact holes by CVD or the like, a film may not be formed evenly and a seam or void may be generated inside some contact plugs.
In this case, the contact plugs and magneto resistive elements on the contact plugs lose their surface flatness, causing a problem of degrading the reliability of the magneto resistive elements.